In my prior U.S. Pat. No. 3,744,606 I have disclosed a dual hydraulic or pneumatic coupling for the selective fluidic actuation of two coupling devices such as clutches and/or brakes. In that prior patent I have also referred to several earlier U.S. patents, owned by the assignee of the present application, which described a variety of planetary-gear transmissions adapted to be used in such a system, generally in series with a hydraulic torque converter. Selection of three forward speed ratios and one reverse ratio is possible in such systems with the aid of two clutches and two brakes associated with two cascaded planetary-gear trains; with the addition of further planetary-gear trains and coupling devices, the number of available speed ratios can be extended. Typically, the two clutches serve for selectively connecting an input shaft (normally driven from the engine through the aforementioned torque converter) with either or both of the two output shafts carrying, for example, the sun gears of a pair of cascaded planetary-gear trains; the coaxially nested output shafts are in line with the input shaft. With the extremities of the nested output shafts suitably staggered, they can be alternatively or jointly coupled with an adjoining extremity of the input shaft while one of these output shafts, conveniently the outer one, can also be selectively immobilized by an associated brake.
Certain problems have heretofore arisen in the feeding of high-pressure fluid to the two clutch housings for the displacement of their associated pistons, in view of the fact that these clutch housings are positively coupled with respective shafts for joint rotation therewith. The expedient of admitting the fluid to these clutch housings through channels in the associated shafts has the drawback of appreciably weakening the shaft structure, which therefore must be made heavier than would otherwise be required, and also necessitates the provision of special seals on opposite sides of the port through which the high-pressure fluid exits from the shaft.